Gravity administration of fluids by IV infusion, also known as IV therapy, is a widely practiced medical procedure. Drugs and fluids such as blood, plasma, dextrose and isotonic saline solutions are administered to patients in this manner.
In the typical administration set, a container containing the IV solution is provided to the attending medical personnel. The container has a seal which is broken by insertion of a piercing spike on the drip chamber. A flexible tubing line delivers the IV fluid to the patient. The purpose of the drop chamber is to facilitate the determination of flow or drip rate through the tubing. Infusion rates may be regulated by the use of an external pinch valve or roller clamp associated with the tubing for less critical gravity-type infusions.
The procedure involves initially purging the tubing and needle of air by initiating a flow of fluid through the tubing. Once this is done, the needle is then inserted into the venipuncture site, such as a location in the forearm or wrist of the patient, and fluid flow is initiated. Medical personnel will normally adjust a pinch valve or roller clamp to restrict the IV tubing. The number of drops passing through the drip chamber is visually counted or timed. The appropriate flow rate is established by trial and error by progressively restricting or opening the lumen in the tubing using the pinch valve or roller clamp. Roller clamps and pinch valves compress the delivery tubing and are not very accurate as they deform the tubing due to the physical properties of the tubing, the inner diameter may change during use.
The administration procedure described above requires the attention of medical personnel for a substantial period of time. However, once a drop rate is set, the rate can be subject to substantial deviation as a result of a number of factors. As the administration of the IV progresses, the fluid level within the solution container will lower, reducing the effective head pressure, causing the drop rate to reduce. The drop rate may also be significantly affected by a change in the elevation of the container or by movement of the patient. Accordingly, the traditional clamping procedures are subject to error and deviation and may deliver fluid at too low or too high a rate which may be adverse to the patient, particularly critical care patients.
Accordingly, various approaches can be found in the prior art to maintaining constant IV flow rates in gravity systems. Flow can be regulated by controlling pressure or resistence either mechanically or electro-mechanically. For example, U.S. Pat. No. 4,343,305 discloses an adjustable rate, constant output infusion set having a connector piece connectable to a container and a headpiece rotatably attached to the connector to adjust the flow rate. An elastically stretchable diaphragm is interposed between the connector piece and the head piece. The connector piece forms a first chamber with a diaphragm which is in direct communication with the container by an inlet port. The headpiece forms a second chamber with a diaphragm, which is in communication with the patient by a control board. The headpiece is rotatably attached to the connector to adjust the flow rate. A passageway connects the first chamber and the second chamber and the diaphragm and by virtue of elasticity maintains a constant pressure drop between the chambers so that the fluid passes the control port at a constant rate of flow.
U.S. Pat. No. 4,515,588 shows a flow regulator for use in an IV administration arrangement which establishes and maintains the rate of flow regardless of changes of pressure. The regulator utilizes a diaphragm control orifice and bypass with a valve to establish the flow rate. The diaphragm adjusts the effective orifice opening to maintain the constant flow selected by the valve setting.
U.S. Pat. No. 4,769,012 discloses a flow regulating device for gravity infusion and transfusion of fluids which has an upper and lower housing and having inlet and outlet channels respectively. A continuously adjustable valve is connected between the inflow and outflow channels. The outflow channel has an outlet opening which defines a valve seat and a a membrane extends across the outlet opening and is movable toward and away from the outlet opening, depending on pressure occurring on opposite sides of the membrane. In this way, extraneous factors such as patient venous pressure can be compensated by the membrane to maintain substantially constant flow of fluid once the valve is set.
U.S. Pat. No. 5,240,035 discloses a pressure compensator for maintaining essentially constant flow rates in an IV system having a source of IV fluid and a controller. The compensator is connectable to the controller and has a housing with a flexible membrane extending transversely therein defining opposite control chambers. One control chamber communicates with the source of IV fluid and also connects to the inlet of the flow controller. The second control chamber receives the regulated flow from the control valve. The second control chamber is generally conical or convex, sloping to an outlet port which is connected to the tubing line leading to the patient. The outlet from the second chamber is smaller than the inlet to the second chamber and the diaphragm serves to control flow to the patient by compensating for pressure changes, such as change in fluid head. The configuration of the second chamber and the configuration of the outlet in the second chamber minimize air entrapment and provide greater flow capacity.
While devices of the type described above improve accuracy in IV delivery systems, there nevertheless exists a need for a cost-effective, reliable, accurate and effective IV regulator which will maintain a substantially constant flow of IV fluid once a flow rate is set. There further exists a need for a device which requires minimal manipulation so that when the regulator is placed in use in an IV administration system, the requirement for drop counting and readjustment is either minimized or eliminated.